Wheel support rolling bearing units are used for rotatably supporting a vehicle wheel and a disk or a drum serving as a rotary member for braking on a knuckle serving as a suspension system. FIG. 21 shows an example of a widely known wheel support rolling bearing unit 1 for a driven wheel (in FR and MR vehicles, a front wheel; in an FF vehicle, a rear wheel). In this wheel support rolling bearing unit 1, a hub 3 is rotatably supported in a radially inner side of an outer ring 2 via a plurality of rolling elements 4, 4. When in use, the outer ring 2 is connected and fixed to a knuckle, while a wheel and a braking rotary member are supported on and fixed to the hub 3 respectively. The wheel and the braking rotary member are supported on the knuckle such that they rotatable with respect to the knuckle.
The outer ring 2 includes double-row outer ring raceways 5, 5 which are formed on an inner peripheral surface of the outer ring 2. On an axially inward portion of an outer peripheral surface of the outer ring 2 (throughout the specification, “inward” with respect to the axial direction implies closer toward the widthwise center of a vehicle body when in use, and “outward” with respect to the axial direction implies closer toward the outside the vehicle body in the width direction when in use), a mounting portion 6 is formed as an outward flange portion.
The hub 3 includes double-row inner ring raceways 8, 8 which are formed on an outer peripheral surface of the hub 3. On a portion of the outer peripheral surface of the hub 3 near an outer end that projects outwardly in the axial direction than the outer ring 2, a support flange 7 is formed as an outward flange portion for supporting and fixing the wheel and the braking rotary member. Between the outer ring raceways 5, 5 of the outer ring 2 and the inner ring raceways 8, 8 of the hub 3, a plurality of rolling elements 4 is arranged in each of the raceways, whereby the hub 3 is rotatably supported on the radially inner side of the outer ring 2.
The hub 3 includes a hub body 9, an inner ring 10 and a nut 11, while the inner ring raceways 8, 8 are formed on an intermediate portion of the hub body 9 and on an outer peripheral surface of the inner ring 10. The inner ring 10 is fitted onto a small diameter step portion 12 formed on a portion the hub body 9 near an axially inner end, and is fixed to the hub body 9 by the nut 11. Here, there is also widely known a structure in which the inner ring 10 is fixed to the hub body 9 using a riveting portion formed in the inner end portion of the hub body 9.
A bearing ring with an outward flange, which is a kind of an outwardly flanged metal member such as the outer ring 2 and hub body 9, can be manufactured by executing plastic working on metal material such as carbon steel. This plastic working method is conventionally widely known, for example, in Patent Documents 1 and 2.
FIG. 22 shows how to manufacture the hub body 9 by plastic working (warm or hot forging). Firstly, a long stock produced by rolling or the like is cut into a given length, thereby obtaining a cylindrical blank 13 shown in FIG. 22(A). Next, according to upsetting in which the blank 13 is compressed in the axial direction, there is provided a first intermediate work 14 of a beer barrel shape shown in FIG. 22(B). Next, according to a rough forming process in which, while the axially half portion of the first intermediate work 14 (in FIG. 22, the lower half portion of the blank 14; that is, the axially inner half portion of the hub body 9 after completed) is pushed into a mold (a die) having a given inner peripheral surface shape, the outside diameter of the axially half portion of the blank 14 is reduced, there is provided a second intermediate work 15 shown in FIG. 22(C). Next, according to a finish forming process in which, in a state where the second intermediate work 15 is set within a mold (a die) having a given inner peripheral surface shape, a punch is pressed against the axially other end face of the second intermediate work 15 (in FIG. 22, the upper end face of the blank 15; that is, the axially outer end face of the hub body 9 after completed) to dent the axially other end face, and also metal material of the second intermediate work 15 is caused to flow outwardly in the radial direction, thereby providing a third intermediate work 16 shown in FIG. 22(D). Since a flash 17 is formed in the surface of the third intermediate work 16 against which the die is butted, the flash 17 is removed by trimming, thereby providing a fourth intermediate work 18 shown in FIG. 22(E). Machining and grinding are carried out on the fourth intermediate work 18, thereby producing the hub body 9.
As the support flange 7 of the thus produced hub body 9, conventionally, there is generally used a disk shaped support flange 7 shown in FIG. 23(A). In the case that a disk shaped support flange 7 is formed according to the finish forming process shown in FIGS. 22(C)→(D), the flash 17 is generated along the entire perimeter of the outer peripheral edge of the support flange 7. Since the width of the flash 17 is narrow and the amount of scrap to be removed in the above-mentioned trimming operation is small, worsening of the yield of the material is limited. Also, a so called flashless working operation, which can prevent a flash, which needs to be removed, from being formed, can be carried out relatively easily.
On the other hand, in recent years, in order that the running performance of a vehicle such as the running comfort and running stability of the vehicle can be enhanced due to the reduced load of a spring, and also in order to reduce the cost of the outwardly flanged metal member due to the reduced cost of the material thereof, as shown in FIG. 23(B), there is proposed a hub body 9a which includes a radial support flange 7a in the outer peripheral surface thereof.
When finish forming process as shown in FIGS. 22(C)→(D) is carried out in order to produce this hub body 9a including a support flange 7a in which a plurality of protrusions 19, 19 are arranged radially, a large flash 17, 17a is formed as shown in FIG. 22(D) and FIG. 24(A). That is, the flash 17, 17a is formed not only in the outer peripheral edge portions of the respective protrusions 19, 19 of the support flange 7a but also between the protrusions 19, 19 adjacent to each other in the circumferential direction. Such a large flash 17, 17a, after execution of the finish forming process, is removed by a trimming operation which is carried out in FIGS. 22(D)→(E) and FIGS. 24(A)→(B), and are then wasted as a scrap piece 20. Even when the scrap pieces 20 are collected together and are reused, the yield of the material is worsened to cause an increase in the cost of the hub body 9a. Therefore, it is not desirable that the amount of scrap pieces 20 increases.
Here, the problem described above is raised not only when producing the hub body 9a having the radial support flange 7a in the outer peripheral surface thereof but also in a case where an outer ring 2 including a non-circular outwardly flanged mounting portion 6 (shown in FIGS. 25(A) and (B)) in the outer peripheral surface thereof is formed by hot forging or by warm forging.    Patent Document 1: Japanese Patent Publication No. JP 2006-111070 A    Patent Document 2: Japanese Patent Publication No. JP 2005-83513 A